In devices that need to store information such as, for example, data storage devices, user data is typically stored on tracks of a storage media. In addition to the user data, position data is also provided on the storage media. The position data can include servo marks that, when read, generally indicate position coordinates (e.g. X, Y coordinates, track number, or sector number) of a transducer relative to the storage media surface. Such devices also include a servo system that positions the transducer over a selected track based on feedback of the position data. The servo system may have a “seek mode” that moves the transducer from one track to another track based on reading the servo marks. The servo system also may have a “tracking mode” in which the transducer is precisely aligned with a selected track based on a reading of the servo marks.
At the time of manufacture of a magnetic data storage device, the servo marks are provided on the storage media. During operational use of the magnetic data storage device, the transducer reads the servo marks but there is typically no need to erase and rewrite servo data during operation. The position of servo marks on the media for a magnetic data storage device is therefore stable and does not change significantly during the operational life of the data storage device.
Data storage devices are being proposed to provide smaller size, higher capacity, and lower cost data storage devices. One particular example of such a data storage device is a ferroelectric probe storage device. The probe storage device may include one or more transducers (e.g. one or more probes), that each includes a conductive element (e.g., an electrode), which are positioned adjacent to and in contact with a ferroelectric thin film storage media. User data is stored in the media by causing the polarization of the ferroelectric film to point “up” or “down” in a spatially small domain local to a tip of the transducer by applying suitable voltages to the transducer through the conductive element. Data can then be read by, for example, sensing current flow during polarization reversal.
For probe storage devices, position data can be written in domains polarized on the ferroelectric storage media. However, the characteristics of probe storage do not permit stable positioning of the position data. When data is read from a ferroelectric storage media with a transducer, the conventional process of reading the data inherently erases or removes the data from the media. An electronic circuit that provides the read operation for a probe storage device must follow up and automatically provide a subsequent write operation of the same data in order to avoid loss of the data on the ferroelectric storage media. This is not an insurmountable problem for user data. However, with position data (e.g. servo marks) the repeated reading and automatic rewriting of position data will inevitably lead to loss of accurate position information. This instability and loss of accurate position information limits the useful life of the probe storage device. Adjacent tracks on the ferroelectric storage media with user data will become misaligned due to creep of the position data and user data tracks will eventually overwrite or interfere with one another.